[Noisebridge-discuss] Disaster Recovery SDR-based mesh
juul at labitat.dk
Fri Sep 13 22:00:06 UTC 2013
On Thu, Sep 12, 2013 at 11:47 PM, Matthieu Tourne <matthieu.tourne at gmail.com
> On Thu, Sep 12, 2013 at 7:33 PM, Marc Juul <juul at labitat.dk> wrote:
>> Some of us at sudo room / east bay mesh are working on a low bandwidth
>> disaster recovery mesh project based on software defined radios.
>> We're prototyping with a combination of USRP1 and RTL-SDR devices and GNU
>> We're having some issues getting the receivers to demodulate our data
>> streams (using DQPSK and QAM modulation).
> I never thought about doing much more than tuning to FM radios with my
> rtl-sdr, but that's a pretty cool project!
Thanks! You should come hack with us!
> I think that depends what's your goal, if you want to decode qpsk frame
> from classic radios  I think rtl-sdr can do it.
> If you want to Tx/Rx data accurately, I think you need a digital
> modulation chip 
> (my understanding is that it works best at the hardware level if you want
> a decent bandwidth)
The RTL-SDR is definitely not a high quality SDR, but we have very low
bandwidth requirements. For the transmitters we're only using USRPs while
prototyping. We're also working on a cheap transmit-only SDR circuit, but
that is definitely a longer term project and for now we just want a full
> Something like this  could help, if you know someone who can program
> fpga cards ..
That's lower cost than the USRP, but still more expensive than we'd like.
> But it's a pretty cool project, maybe you can use an OFDM stream instead
> That's the hd tv data stream the chip RTL2832U  in the rtl-sdr is meant
> to demodulate in hardware.
I hadn't actually considered using the built-in de-modulation :-S I'll look
> .. I even found an opencore for ofdm modulation , which could (in
> theory) be loaded on an fpga ..
Interesting. Thanks for all the links!
>  http://en.wikipedia.org/wiki/Project_25
>  http://www.maximintegrated.com/app-notes/index.mvp/id/686
>  http://nuand.com/
>  https://www.youtube.com/watch?v=TQ0KDjxhXNk
>  http://opencores.org/project,ofdm
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